1. Field of the Invention
The present invention relates generally to aerodynamic devices for use with vehicles, such as trucks and semi-trailers, and in particular relates to an aerodynamic wind drag reduction device or airfoil for attachment to the rear of a truck or trailer and moveable between a storage configuration and a deployed configuration.
2. Description of the Prior Art
As vehicles such as tractor-trailers and transport trucks move at highway speeds, air flows rapidly along the top and sides of the vehicle or trailer. When this air reaches the end of the trailer, it has too much momentum to make an immediate turn to follow the contour around the rear surface of the trailer, such that the air flow becomes detached creating a low pressure area behind the trailer. This low pressure region acts as a vacuum, pulling on the back of the trailer and resisting forward motion. This resistance is called base drag, which ultimately results in lower fuel economy. Studies have estimated that base drag may account for 10 percent of a tractor-trailer""s fuel consumption at speeds over 55 mph.
Base drag on trailers could be eliminated if the end of the trailers were provided with a different shape such as a tear drop or half egg shape, in which case the air would flow smoothly and remain attached to the rear of the trailer, minimizing any low pressure region behind the trailer. However, trailers are designed to carry a maximum amount of freight for a given legal weight, width and height, such that economics tend to restrict trailer designs to xe2x80x9cboxyxe2x80x9d shapes with poor aerodynamics. In addition, trailers are normally loaded and unloaded through doors at the rear of the trailer, requiring that the rear of the trailer be provided with a conventional flat surface to accommodate the doors.
Federal regulations permit a drag reduction device up to five feet in length to be added to a trailer, without counting against the trailer""s length limit. Thus, the base drag reduction devices proposed to-date have typically been designed as xe2x80x9cadd-onxe2x80x9d devices, which attach to the rear of the trailer. Unfortunately, these devices generally have not achieved widespread use. In order for a drag reduction device to be widely adopted by the trucking industry, it must not only be aerodynamically effective, but also must meet several criteria relating to the durability and convenience of use of the device. These criteria include: the ability to survive in a difficult environment, including salt spray, ice, road shocks and wind gusts; the ability to deploy and collapse automatically, in that drivers of large fleets do not pay for fuel and cannot be counted on to manipulate a manual device; resistant to damage as trailers are backed into docks, other trailers, or other stationary objects; must be essentially maintenance-free; and must pose no safety risk to other motorists.
Prior art devices include various mechanisms for providing folding frames to define the contour of the airfoil, or for providing an inflatable airfoil which collapses when the vehicle is not in motion. There is a continuing recognized need for providing a drag reduction device including a convenient mechanism for extending and retracting the device, and which will not unduly alter the structure of the trailer or require extensive modifications, and further which requires a minimum number of components resulting in easier and faster deployment and in reduced cost.
The present invention provides a device or airfoil for decreasing the base drag behind a truck or trailer in order to improve the fuel economy of the trailer. The device is designed to be moveable between a storage configuration and a deployed configuration, and is further designed for automatic operation without manual manipulation of a mechanism by an operator. In addition, the device is designed, in its storage configuration, to be configured to lie closely adjacent to the rear doors of a trailer. Further, the device is designed to provide a curved aerodynamic shape for minimizing the low pressure area behind the trailer when in its deployed configuration.
In accordance with one aspect of the invention, an airfoil is provided to reduce wind resistance of trucks and semi-trailers having a substantially planar rear surface, the airfoil being deployable from a storage configuration to a deployed configuration and comprising: first and second side panels supported at the rear surface; each of the first and second side panels comprising laterally spaced proximal and distal edges, each of the proximal edges defining a pivot edge for pivotally attaching a respective one of the first and second panels adjacent a side of the planar rear surface; each of the first and second side panels including a fold area extending substantially vertically and located intermediate the proximal and distal edges; and wherein the first and second side panels are moveable from the storage configuration located adjacent the rear surface to a deployed configuration extending outwardly from the rear surface, the side panels each folding at the fold area when the side panels are in the storage configuration.
In a further aspect of the invention, an airfoil is provided to reduce wind resistance of trucks and semi-trailers having a substantially planar rear surface, the airfoil being deployable from a storage configuration to a deployed configuration and comprising: first and second side panels supported at the rear surface; each of the first and second side panels comprising laterally spaced proximal and distal and top and bottom edges, each of the proximal edges defining a vertical pivot edge for pivotally attaching a respective one of the first and second panels adjacent a side of the planar rear surface, such that the side panels are pivotally moveable between the storage configuration and the deployed configuration; top and bottom end panel structures, each of the end panel structures including a proximal edge defining a horizontal pivot edge for pivotally attaching a respective one of the top and bottom panels adjacent a top and bottom of the rear surface, the end panel structures including outer edges moveable from the storage configuration adjacent the rear surface to the deployed configuration extending outwardly from the rear surface; and an actuation system comprising at least one flexible structure extending from a side of the rear surface and having an end connected to one of the panels of the airfoil wherein the flexible structure is moveable between an extended and a retracted position to actuate the airfoil in movement between the storage configuration and the deployed configuration.
In accordance with an additional aspect of the invention, an airfoil is provided to reduce wind resistance of trucks and semi-trailers having a substantially planar rear surface, the airfoil being deployable from a storage configuration to a deployed configuration and comprising: a first set of panels pivotally movable toward and away from each other; a second set of panels pivotally movable toward and away from each other in a direction perpendicular to a direction of movement of the first set of panels; the first set of panels being located folded under the second set of panels when in the storage configuration; and the first set of panels actuated for outward pivotal movement from the storage to the deployed configuration, and located for engagement with the second set of panels whereby actuation of the first set of panels from the storage to the deployed configuration includes the first set of panels engaging and pushing outwardly on the second set of panels to move the second set of panels to the deployed configuration.